1. Field of the Invention
The present invention concerns a method and device to assisting in the extraction of a tissue sample, i.e., to implement a biopsy.
2. Description of the Prior Art
In a biopsy a tissue sample (for example from the breast of a patient) is extracted and histologically examined. The tissue extraction for the most part takes place with the assistance of an imaging method.
One imaging method in mammography for the diagnosis of breast cancer is stereotactic imaging. For this, the breast is compressed and fixed with a compression device in a mammography apparatus. Whether the region to be examined is suitable for a diagnostic—i.e. whether it contains the lesion discovered in the clarification mammogram—is checked with a first x-ray acquisition. A second and third x-ray exposure are subsequently made from a positive and negative angle relative to the first x-ray exposure in order to calculate from these the spatial arrangement of the target, for example of a tumor or its micro-calcifications. After this the biopsy needle is introduced into the breast and the position of the biopsy needle is monitored with an additional stereo exposure.
In a further imaging method, slice images of a tomosynthesis method are used to assist in diagnostics and to determine the spatial coordinates for an extraction of a tissue sample. In tomosynthesis methods a tomosynthesis reconstruction process is applied with which a volume data set of a subject is created. The volume data set includes slice images in which tissue variations can be localized and assessed. A sequence of, for example 25 x-ray images is created to implement the tomosynthesis. For this purpose, an x-ray source is moved across a detector, for example in an angle range between +25° and −25° on a circle segment. The radiation of the x-ray source is triggered at regular intervals and an x-ray image is read out from the detector and cached. A number of slice images extending parallel to the detector and stacked along a line perpendicular to the detector are subsequently created on the basis of the x-ray exposures in a tomosynthesis method, for example. Depending on examination- and apparatus-specific limitations in the deflection of the x-ray source, a depth resolution (i.e. the resolution along the perpendicular line) is lower relative to the resolution that can be achieved horizontally. This has the disadvantage of an imprecision in the determination of the spatial coordinates for a biopsy. However, the depth resolution of tomosynthesis is still better than that of stereotaxis, so the uncertainty in the coordinate determination is also less.